A 2-hydroxy-4-(methylthio)butyrate compound represented by the formula (2):
wherein A is a hydrogen atom or a group represented by R—CH2—, wherein R is a hydrogen atom or an alkyl group, is known as a starting material for synthesizing analogs of L-methionine, the essential amino acid, or penem antibiotics (see U.S. Pat. No. 4,524,077 and EP 338735 A). As a process for producing a typical compound thereof, 2-hydroxy-4-(methylthio)butyric acid, JP 5-1787 B discloses the reaction of 3-(methylthio)propionaldehyde and hydrogen cyanide to obtain 2-hydroxy-4-(methylthio)butyronitrile, followed hydrolysis of the 2-hydroxy-4-(methylthio)butyronitrile thus obtained with a strong acid such as sulfuric acid. Also, JP 2006-136317 A discloses a process using 1,2-epoxy-3-butene as a staring material.